1. Field of the Invention
The present invention relates to a liquid injection device and an inkjet recording device including the same, and more specifically, to a control technology for liquid injection adopting a so-called multi-dot system.
2. Description of the Related Art
A liquid injection device used for an inkjet recording device or the like includes a liquid injection head injecting a liquid drop and a control device controlling the liquid injection head. For example, an ink injection head in an inkjet recording device includes a pressure chamber temporarily storing ink, an actuator that is in contact with the pressure chamber and includes a piezoelectric element, and a nozzle that is in communication with the pressure chamber and injects an ink drop toward a recording medium such as a recording paper sheet or the like. Such an inkjet recording device is operated as follows. When a driving pulse is transmitted to the actuator, the piezoelectric element is contracted or extended based on the driving pulse. As a result, the interior of the pressure chamber is expanded or contracted to inject ink in the pressure chamber from the nozzle. The injected ink drop lands on the recording medium, and thus one dot (drop corresponding to one pixel) is formed on the recording medium.
In such an inkjet recording device, there is a limit on the amount of liquid contained in one liquid drop that can be stably injectable by one driving pulse. Thus, various studies have been made conventionally in order to realize gray scale printing. For example, Japanese Laid-Open Patent Publication No. 2014-162221 discloses a method for driving an ink injection head by which the size of dots is adjusted by a multi-dot system. By the multi-dot system, a driving signal including a plurality of driving pulses in one liquid drop injection period for forming one dot is generated. From the plurality of driving pulses, one or at least two driving pulses are selected in accordance with the size of the dot, and are supplied to the actuator driving the ink injection head. For example, for forming a relatively large dot, two or more ink drops are injected in a time-series manner in one liquid drop injection period. These ink drops are merged before landing on the recording medium, or are caused to land on the same position on the recording medium.